Project description:The programmed formation of hundreds DNA double strand breaks (DSBs) is essential for proper meiosis and fertility. In mice and humans, the location of these breaks is determined by the meiosis-specific protein PRDM9, through the DNA binding specificity of its zinc finger domain. PRDM9 also has methyltransferase activity. Here, we show that this activity is required for H3K4me3 and H3K36me3 deposition and for DSB formation at PRDM9 binding sites. By analyzing mice that express two PRDM9 variants with distinct DNA binding specificities, we reveal severalthe basic principles of PRDM9-dependent DSB site determination, in which an excess of sites are designated through PRDM9 binding and subsequent histone methylation, from which a subset are selected for DSB formation.
Project description:PRDM9 specifies the sites of meiotic DNA double strand break that initiate meiotic recombination in mice and humans. PRDM9 is known to bind to specific DNA sequences with its DNA binding domain, to induce H3K4me3 and H3K36me3 to adjacent nucleosomes through its methyltransferase activity, and to recruit or activate the meiotic DSB machinery. To understand how PRDM9 executes these various steps, we set up to identify its partners. This was performed by a proteomic approach where protein extracts from mouse testis were immunoprecipitated with anti-PRDM9 antibody for mass spectrometry analysis.
Project description:A hallmark of meiosis is the rearrangement of parental alleles to assure genetic diversity in gametes. These chromosome rearrangements are mediated by the repair of programmed DNA double-strand-breaks (DSBs) as genetic crossovers between parental homologs. In mice, humans, and many other mammals, meiotic DSB occur primarily at hotspots, determined by sequence-specific binding of the PRDM9 protein. Without PRDM9, meiotic DSBs occur near gene promoters and other functional sites. Studies in a limited number of mouse strains showed that functional PRDM9 is required to complete meiosis, but despite its apparent importance, Prdm9 has been repeatedly lost across many animal lineages. Both the reason for mouse sterility in the absence of PRDM9 and the mechanism by which Prdm9 can be lost remain unclear. Here, we explore if mice can tolerate the loss of Prdm9. By generating Prdm9 functional knockouts in an array of genetic backgrounds, we observe a wide range of fertility phenotypes and ultimately demonstrate that PRDM9 is not required for completion of meiosis. Although DSBs still form at a common subset of functional sites in all mice lacking PRDM9, meiotic outcomes differ substantially. We speculate that DSBs at functional sites are difficult to repair as a crossover and that by increasing the efficiency of crossover formation at these sites, genetic modifiers of recombination rates can allow for meiotic progression. This model implies that species with a sufficiently high recombination rate may lose Prdm9 yet remain fertile.
Project description:PRDM9, a histone methyltransferase, initiates meiotic recombination by binding DNA at recombination hotspots and directing the position of DNA double-strand breaks (DSB). The DSB repair mechanism suggests that hotspots should eventually self-destruct, yet genome-wide recombination levels remain constant, a conundrum known as the hotspot paradox. To test if PRDM9 drives this evolutionary erosion, we compared activity of the Prdm9Cst allele in two Mus musculus subspecies, M.m. castaneus, in which Prdm9Cst arose, and M.m. domesticus, into which Prdm9Cst was introduced. Comparing these two strains, we find that haplotype differences at hotspots leads to qualitative and quantitative changes in PRDM9 binding and activity. Most variants affecting PRDM9Cst binding arose and were fixed in M.m castaneus, suppressing hotspot activity. Furthermore, M.m castaneus x M.m domesticus F1 hybrids exhibit novel hotspots, representing sites of historic evolutionary erosion. Together these data support a model where haplotype-specific PRDM9 binding directs biased gene conversion at hotspots, ultimately leading to hotspot erosion. Identify position of meiotic H3K4me3 from various sub-species of mice and F1 hybrids from crosses between subspecies. In addition, perform ChIP-seq analysis on the meiosis-specific methyltransferase PRDM9.
Project description:Meiotic recombination starts with the formation of DNA double-strand breaks (DSBs) at specific genomic locations that correspond to PRDM9-binding sites. The molecular steps occurring from PRDM9 binding to DSB formation are unknown. Using proteomic approaches to find PRDM9 partners, we identified HELLS, a member of the SNF2-like family of chromatin remodelers. Upon functional analyses during mouse male meiosis, we demonstrated that HELLS is required for PRDM9 binding and DSB activity at PRDM9 sites. However, HELLS is not required for DSB activity at PRDM9-independent sites. HELLS is also essential for 5-hydroxymethylcytosine (5hmC) enrichment at PRDM9 sites. Analyses of 5hmC in mice deficient for SPO11, which catalyzes DSB formation, and in PRDM9 methyltransferase deficient mice reveal that 5hmC is triggered at DSB-prone sites upon PRDM9 binding and histone modification, but independent of DSB activity. These findings highlight the complex regulation of the chromatin and epigenetic environments at PRDM9-specified hotspots.
Project description:Meiotic DSB, catalyzed by the Spo11 transesterase protein and accessory DSB proteins, form in the nucleosome depleted regions (NDR) at promoters, preferentially those located on the chromosome loops that shape meiotic chromosomes, whereas the DSB proteins are located on chromosome axes at the basis of these loops. Mechanisms bridging these two chromosomal regions for DSB formation have remained elusive. Here we show that Spp1, a conserved member of the histone H3K4 methyltransferase Set1 complex, is required for normal levels of DSB formation and is associated with chromosome axes in the DSB-rich domains during meiosis. Moreover, Spp1 physically interacts with the Mer2 axis-associated DSB protein, and uses its PHD finger as a magnet to read H3K4 trimethylation close to promoters, tether these regions to chromosome axes and activate cleavage in the nearby promoter by the DSB proteins. We further show that in the absence of Spp1 or the Set1 complex, DSB are introduced at a few new sites, located in promoters of transcriptionally induced genes, suggesting another selection mechanism of preferred DSB sequences. This paper provides the molecular mechanism linking H3K4me3 to the DSB forming machinery, by the meiosis-specific specialization of Spp1 as an active member of the DSB complex and a reader of H3K4me3, and opens perspectives for the study of DSB formation at mammalian recombination hotspots that are also enriched in H3K4me3. ChIP-chip experiment in vegetative or meiotic diploid SK1 yeast cells - two biological replicates
Project description:Histone H3K4 methylation is a feature of meiotic recombination hotspots shared by many organisms including plants and mammals. Meiotic recombination is initiated by programmed double-strand break (DSB) formation that in budding yeast takes place in gene promoters and is promoted by histone H3K4 di/trimethylation. This histone modification is recognized by Spp1, a PHD-finger containing protein that belongs to the conserved histone H3K4 methyltransferase Set1 complex. During meiosis, Spp1 binds H3K4me3 and interacts with a DSB protein, Mer2, to promote DSB formation close to gene promoters. How Set1 complex- and Mer2- related functions of Spp1 are connected is not clear. Here, combining genome-wide localization analyses, biochemical approaches and the use of separation of function mutants, we show that Spp1 is present within two distinct complexes in meiotic cells, the Set1 and the Mer2 complexes. Disrupting the Spp1-Set1 interaction mildly decreases H3K4me3 levels and does not affect meiotic recombination initiation. Conversely, the Spp1-Mer2 interaction is required for normal meiotic recombination initiation, but dispensable for Set1 complex-mediated histone H3K4 methylation. Finally, we provide evidence that Spp1 preserves normal H3K4me3 levels independently of the Set1 complex. We propose a model where Spp1 works in three ways to promote recombination initiation: first by depositing histone H3K4 methylation (Set1 complex), next by “reading” and protecting histone H3K4 methylation, and finally by making the link with the chromosome axis (Mer2-Spp1 complex). This work deciphers the precise roles of Spp1 in meiotic recombination and opens perspectives to study its functions in other organisms where H3K4me3 is also present at recombination hotspots.
Project description:SPO11 generates hundreds of DNA double-strand breaks (DSBs) to initiate meiotic recombination. Heritability and genome stability are shaped by the nonrandom distribution of DSBs, but mechanisms molding this landscape remain poorly understood. Here we exploit genome-wide maps of mouse DSBs at unprecedented nucleotide resolution to uncover previously invisible spatial features of recombination. At fine scale, we reveal a stereotyped hotspot structure––DSBs occur within narrow zones between methylated nucleosomes––and identify relationships between SPO11, chromatin, and the histone methyltransferase PRDM9. At large scale, DSB formation is suppressed on non-homologous portions of the sex chromosomes via the DSB-responsive kinase ATM, which also shapes the autosomal DSB landscape at multiple size scales. We also provide the first genome-wide analysis of exonucleolytic DSB resection lengths and elucidate spatial relationships between DSBs and recombination products. Our results paint a comprehensive picture of features that govern successive steps in mammalian meiotic recombination.
Project description:In most organisms, meiotic recombination begins with programmed DNA double strand break (DSB) formation by Spo11. Here, we present evidence that Tel1/Mec1, the budding yeast ATM/ATR, regulate DSB formation by phosphorylating Rec114, an essential Spo11-accessory protein. Analyses of a non-phosphorylatable- or phosphomimetic- alleles of rec114 revealed that DSB-dependent phosphorylation of Rec114 limited its association with DSB-hotspots resulting in reduction in DSB formation. Also observed were the impact of Rec114 phosphorylation on its homolog synapsis-associated removal from chromosomes and NDT80-dependent turnover. Specifically, we found that the synapsis- and NDT80-dependent Rec114 downregulation occurred later in the rec114 mutant with a reduced Spo11-catalysis, but earlier in the other with an enhanced catalysis, strongly implicating the existence of a feedback mechanism coupling the extent of Spo11-catalysis to Rec114 activity. Taken together, these observations suggest that three different mechanisms of down regulating Rec114 contribute to meiotic DSB homeostasis, a feedback mechanism to maintain the number of meiotic DSBs at the developmentally programmed level. 6 genome wide ChIPchip sets: 3 for meiotic DSB formation (Spo11-ChIP) and 3 for protein-DNA association (Rec114-ChIP), each for wild type and two mutants during meiosis (corresponding to the main Figure 3, as well as to Figures S3, S4, S5).
Project description:The locations of mammalian recombination hotspots are determined by PRDM9, a zinc finger histone methyltransferase that locally trimethylates histone H3 at residues K4 and K36. Here we report Prdm9-EP, a glu365pro mutation that severely reduces catalytic activity in vivo. This mutation causes sterility with complete meiotic arrest in homozygous males, while homozygous females are able to produce live offspring in natural matings. These H3K4me3 ChIP-seq data from Prdm9-EP homozygous spermatocytes show the extent to which H3K4 methyltransferase activity is compromised by this mutation, while the DMC1 ChIP-seq data show its effect on meiotic double-strand breaks in spermatocytes. For comparison, we mapped previously reported H3K4me3 ChIP-seq data from wild-type C57BL/6J spermatocytes (GSE52628) to mm10, merging the two biological replicates (SRX381465 and SRX381466) before mapping, and proceeding with processing. We did the same with published DMC1 ChIP-seq data, merging three previously reported DMC1 ChIP-seq biological replicates, isolated from wild-type C57BL/6N males (GSE112110; SRX3825301, SRX3825302, and SRX3825303). Processed data files are presented here.